Cathode-ray tube



May 2, 1961 Filed Nov. 4, 1957 A. G. VAN DOORN CATHODE-RAY TUBE 2 Sheets-Sheet 1 INVENTOR ADRIAAN GERARDVAN DOORN BY J J J AGEN y 2, 1961 A. G. VAN DOORN 2,982,874

CATHODE-RAY TUBE Filed Nov. 4, 1957 2 Sheets-Sheet 2 INVENTOR AERIAAN GERARD VAN DOORN AGENT V edges of the picture.

CATHO E-BAY TUBE Adriaan Gerard Van Doorn, Eindhoven, Netherlands,

assignor to North American Philips Company, Inc New o k, N co poration of Delaware Filed Nov..4,' 1957, Ser. No. 694,299 4 v Claims priority, application Netherlands Nov. 15,1956 4 Claims. ((1313978) age difference between the grids -in a manner such that it strikes alternately the three phosphor lines. It appears that according as the beam is directed further to the edge of the picture screen deviations occur in the deflection sensitivity: towards the edges this deflection sensitivity is found to increase, if the screen and the grids are flat and extend parallel to one another. Since the deflection sensitivity depends upon the distance between grids and screen, the said deviation can be compensated in the direction at right angles to the direction of the grid wires by arranging, in the case of a flat screen, the grid wires in a cylindrical plane in a manner such that the distance between grid and screen decreases towards the A compensation in the direction of length of the grid wires cannot be obtained in this manner, since it is practically impossible to have the taut grid wires curved. The screen could, however, be made cylindrical, so that also in this direction the distance between grid and screen is smaller at the edges of the picture than in the centre. With such a construction, however, the compensation obtained by the cylindrical shape of the grids is aifected adversely, since the axes of the cylinders of the screen and the grids are at right angles to one another and their concave sides are facing one another. As an alternative, flat grids may be combined with a slightly spherical screen, but also this solution iscomplicated, since such a slightly spherical screen in a bulb having a more convex window gives rise to unwanted light reflections and difliculties in mounting. Even a direct application of thescreen to the window does not bring about a solution, since, a solid construction requires such a strong spherical curvature of the window that a material overcompensation is involved, which requires a compensation in the opposite direction.

In accordance with the invention the said difliculties are obviated in such a tube in that the grid wires are arranged in a cylindrical plane or surface and have a thickness which varies from the centre towards the edges.

If use is made of a flat screen, the grid wires may thus be arranged in a cylindrical plane, of which the concave side faces the screen, while the wires themselves are thicker in the centre than at the ends. If, on the contrary, the screen is applied to the spherical window of the tube, the grid wires must lie in a cylindrical plane which is curved in the same direction as the screen, but which has a larger radius of curvature, while, in accordv by drawing them gradually upwards.

2,982,874 Patented May 2, 1961 a'nce with the invention, the grid wires are thinner in the centre than at the ends, towards which their thickness increases gradually.

Such grids can be manufactured by immersing them, subsequent to winding of the wires, in the first-mentioned case, in an etching bath down to half their length and Thus the wires grow thinner towards the ends. Then the other half of the grids is treated in the same manner. In the other case case the grids are immersed first with one half and then with the other in a metal plating bath, in which metal is deposited on the wires. By withdrawing the grids slowly out of the bath, the wires canbe made thicker at the ends than in the centre; The decrease or increase in wire diameter may be linear or non-linear by controlling the rate of withdrawal of the grid wires and/orby means of the current intensity of the'bath.

The invention will-be described more fully with reference toa drawing, in which:

Fig. 1 shows part of a cathode-ray tube having a flat screen, and

Fig. 2 shows part of such a tube, in which the screen is applied directly to the inner side of the window.

Fig, 3 is a cross-sectional view at right angles to that of Fig. 1.

Fig. 4 is a cross-sectional view at right angles to that of Fig. 2.

7 Referring to Figs. 1 and 3, reference numeral 1 designates the bulb or envelope and 2 the window or faceplate of a cathode-ray tube. The bulb contains a fiat glass plate 3, to which is applied the phosphor screen 4 consisting of different colour lines. Close in front of the phosphor screen 4 are arranged the colour switching grids 5, of which the wires 6 are thicker in the centre than at the ends. The grids 5 are curved cylindrically (as shown in Fig. 3) so that the hollow side faces the screen 4.

The grid wires may be made thinner by etching from the centre towards the ends. The grid-screen unit is fastened in the bulb 1 in a manner not shown.

Referring to Figs. 2 and 4, the phosphor screen 4 is applied directly to the window 2. The grids 7 are curved cylindrically so that the hollow side is remote from the screen 4. The grid wires 8 are thickened towards the ends by means of a metal-plating bath, so that the overcompensation of the deflection sensitivity, which is due to the fact that the distance between grids and screen required for the compensation inaccordance with Fig.

1', can be obviated. If the window had just the spherical shape required for the compensation, a very thick wall had to be used particularly for larger tubes, which would render the tube very heavy and involve difliculties in the pressing operation.

The grid wires may be immersed slowly into the bath and be drawn up rapidly or conversely. As an alternative, both the immersion and the withdrawal may be performed slowly. The eflect in accordance with the invention may be obtained not only by variation in wire diameter, but also by flattening the wires partly in a manner such that the projection of the flattened wire portions on the screen is at a minimum at the areas where the wire diameter must be at a maximum. Then the flattened wire portions operate as narrow deflection plates. e

As a specific example, the wire diameter or the width of the projection of the wires on the screen should vary between 50 and in order to ensure an adequate compensation of the deflection sensitivity.

What is claimed is:

1. A colored-image-producing cathode-ray tube comprising an electron-beam-producing gun, a beam-receiving screen having groups of lines of color phosphors, and beam-switching means disposed in front of the screen and comprising a pair of grids having substantially coplanar, interleaved wires and adapted to deflect the beam to impact a selected color line in accordance with varying potentials applied thereto, said interleaved wires lying in a generally cylindrically-curved surface whose axis extends parallel to the wires and said wires having varying diameters from their center toward their ends, whereby the deflection sensitivity of ,the beam-switching means is substantially uniform over the whole surfac of the grids.

' 2. A cathode-ray tube as set forth in claim 1 wherein the color lines are parallel to the grid wires, and the pair of grids also serves to focus the beam onto the color lines.

' 3. A colored-image-producing cathode-ray tube comprising an electron-beam-producing gun, a substantiallyplanar beam-receiving screen having groups of lines of color phosphors,- and beam-switching means disposed in front. of the screen and comprising a pair of grids having substantially coplanar, interleaved wires and adapted to aesas'm 4. A colored-image-producing cathode-ray tube comprising an electron-beam-producing gun, a curved beamreceiving screen having groups of lines of colorphosphors, and beam-switching meansdisposed in front of the screen and comprising a pair of grids having substantially coplanar, interleaved wires and adapted to deflect the beam to impact a selected color line in accordance with varying potentials applied'th'ereto, said interleaved wires lying in a cylindrical surface whose axis extends parallel tothe wires and on the side of the wires opposite to that of the'screen so that the convex side of the surface faces the curved screen, said cylindrical surface having a smaller curvature than the screen, said wires. each having a diameter that is larger at both ends substantially uniform over the whole surface of the grids.

deflect the beam to impact a selected color line in ac- References Cited in'the file of this patent V UNITED STATES PATENTS 1,542,386

Hartley e Iune16, .1925 2,075,202 Jonker Mar. 30, 1937 2,640,767 Easley June 2, 1953 2,653,263 Lawrence Sept. 22, 1953 2,722,623 Law Nov. 1, 1955 2,729,760 Lawrence Jan. 3, 1956 2,746,848 Jones May 22, 1956 2,795,720 Epstein June 11, 1957 2,813,213 Crarner Nov. 12, 1957 

